1. Field of the Invention
The present invention generally pertains to the field of reclining seats and is more particularly directed to a mechanism for locking the movable backrest of a reclining seat at a selected angular position within the seat's range of adjustment.
2. State of the Prior Art
Numerous mechanisms have devised in the past for use in reclining seats. In particular, many such devices have been developed and found widespread usage in automotive seats. To an increasing extent, at least the driver's seat and frequently also the front passenger seat in motor vehicles are furnished as adjustable reclining seats as standard equipment. While the high end automobile models offered by every manufacturer are equipped with electrically operated seats capable of being adjusted in height, tilt, and dashboard spacing, as well as seatback inclination, manually operated mechanical reclining seatback locking devices are used in lower cost vehicles in response to rising consumer expectations for reclining seats as standard equipment in all vehicles. Typically, the backrest is spring loaded towards a fully upright position and the recliner locking mechanism locks the backrest against its forward spring loading. The backrest is repositioned by releasing the locking mechanism and then either pushing backwards against the backrest to overcome the backrest loading spring if it is desired to recline the backrest, or by allowing the backrest spring to move the backrest towards a more upright position. When the desired backrest position has been obtained the locking mechanism is engaged for holding the backrest in the selected position
Existing seatback locking mechanism designed for this purpose suffer from undue complexity and consequent high cost, or excessive weight and size. Still other designs achieve relative simplicity at the expense of performance, such as by providing adjustment of the reclinable backrest in fixed increments rather than continuous adjustment to a desired position.
A continuing need exists for a low cost, simple, reliable, manually operated mechanical lock for reclining seats capable of continuous adjustment of the backrest position while maintaining high standards of performance. In particular the locking mechanism must positively restrain the backrest against "creep" and displacement due to vibration, road shock, seat occupant's weight, as well as vehicle acceleration or braking. Such a mechanism must be reliable in daily use over a period of years without maintenance under difficult environmental conditions.
Various continuously positionable locking devices for reclining seats are known, typically including a lower frame assembly which is normally attached to the stationary portion of the seat, and an upper plate element which is pivoted to the frame assembly and affixed to the reclinable backrest, such that the backrest is hinged to the stationary seat portion by means of the plate pivoted to the frame. The pivotable plate has a toothed arcuate lower edge defining a gear rack which is in mesh with a gear wheel rotatably mounted to the frame assembly, such that pivotal movement of the upper plate causes rotation of the gear wheel relative to the frame. It is further known to provide a brake drum wheel, either integral with the aforementioned gear wheel or drivingly connected thereto by means of additional gearing, and a brake spring wound tightly around the brake drum and fixed to the frame so as to normally lock the drum wheel relative to the frame assembly thereby preventing movement of the gear train and consequent pivotal movement of the upper plate, thus locking the backrest. The mechanism is released to permit adjustment of the backrest position by partially unwinding the brake spring to allow rotation of the drum wheel and thereby freeing the gear train and pivotal plate for movement relative to the frame assembly.
While the use of a coil spring as the locking device can result in a low cost, compact and simple mechanism, past designs based on this approach have been deficient in that the brake spring in itself makes only frictional engagement with the brake drum and thus does not assure positive locking of the mechanism against forces acting against the backrest and sufficiently large to overcome the frictional force of the spring. Furthermore, the locking action of the brake spring tends to be more effective for holding the brake drum against rotation in one direction than in the opposite direction. Thus, prior recliner locking devices of this type are constructed so that the brake spring effectively holds the backrest against backward force such as applied by the weight of the seat occupant, but is less effective in holding the backrest against forwardly directed force which is added to the normal spring loading of the backrest, such as applied by a rear seat occupant accidentally or deliberately pushing forward on the backrest, or by road shock and vibration which tends to drive the backrest forward in small increments causing a gradual forward movement of the backrest known as "creep" .
A continuing need therefore exists for an infinitely positionable reclining seat lock mechanism which takes advantage of the simplicity of the brake spring and drum locking action yet overcomes the aforementioned shortcomings of existing devices.